The cutting performance of a metal material usually refers to a performance or quality that a metal material has that can be clearly defined and measured as an indicator of the ease of cutting. Good machinability should be good tool durability or higher cutting speed, lower cutting force, lower cutting temperature, easy to obtain better surface quality and chip shape under a certain degree of durability. Control or break chips easily.
1. Turning movement and the formed surface
Turning motion: In the cutting process, in order to remove excess metal, the workpiece and the tool must be made to perform relative cutting motions. The motion of cutting the excess metal on the workpiece with a turning tool on the lathe is called turning motion, which can be divided into main motion and forward motion. Give exercise.
Feeding movement: the movement of continuously throwing new cutting layers into cutting. The feeding movement is the movement along the surface of the workpiece to be formed, which can be continuous movement or intermittent movement. For example, the turning tool on the horizontal lathe moves continuously during the movement, and the feed movement of the workpiece on the bullhead planer is an intermittent movement.
The surface formed on the workpiece: during the cutting process, the machined surface, the machined surface and the surface to be machined are formed on the workpiece. The machined surface refers to a new surface formed by removing excess metal from the car. The surface to be processed refers to the surface on which the metal layer will be cut off. The machined surface refers to the surface that the cutting edge of the turning tool is turning.
Main motion: directly cut off the cutting layer on the workpiece and turn it into chips, thereby forming the movement of the new surface of the workpiece, which is called the main motion. When cutting, the rotational movement of the workpiece is the main movement. Generally, the speed of the main movement is higher and the cutting power consumed is higher.
Factors affecting the machinability of metal materials.
1. Material toughness
Toughness is expressed by impact value. The higher the toughness of the material, the more energy is consumed during cutting, the cutting force and cutting temperature are also higher, and it is not easy to break chips, so the workability is poor. Some alloy structural steels are not only stronger than carbon structural steels, but also have higher impact values, so they are more difficult to process.
Other physical and mechanical properties also have a certain influence on the machinability. For example, materials with a large linear expansion coefficient will expand and contract during processing, and the size of the workpiece will vary greatly, so it is not easy to control the accuracy. The material with low elastic modulus has a large elastic recovery during the forming process of the processed surface, and it is easy to cause strong friction with the flank surface.
2. The strength and plasticity of the material
In terms of the hardness of the workpiece material (including room temperature hardness and high temperature hardness), in general, the high room temperature hardness of similar materials has low workability. Because when the material hardness is high, the contact length between the chip and the rake face is reduced, so the shear stress on the rake face increases, and the frictional heat is concentrated on the smaller tool-chip contact surface, which promotes the increase of cutting temperature and increased wear. If the hardness is too high, it will even cause burning of the tip and chipping. Take steel as an example, steel with moderate hardness is better processed. In addition, appropriately increasing the hardness of the material is conducive to obtaining better processed surface quality. The plasticity of a material is usually expressed in terms of elongation. Generally, the greater the plasticity of the material, the more difficult it is to process. Because of the large plastic material, processing deformation and hardening, and cold welding of the tool surface are more serious, it is not easy to break chips, and it is not easy to obtain a good, processed surface quality.
The surface quality of the workpiece is closely related to its performance. The performance of the workpiece is the design requirement to ensure the normal operation of the machine. Therefore, in the cnc metal machining, economic benefits should also be considered to ensure the processing of the surface of the workpiece. Quality, to avoid increasing the manufacturing cost of parts and causing unnecessary losses. Only by understanding and mastering the factors that affect the surface quality of mechanical processing can we take corresponding process measures in production practice to reduce processing quality problems caused by surface quality defects of parts, thereby improving the performance, life and reliability of mechanical products.
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