With the continuous acceleration of industrial technology innovation and development, mechanized production mode has gradually replaced manual production in some production fields, especially in the manufacturing industry. Due to the special use environment of some important parts, such as high temperature and high pressure, in order to ensure the stability of parts, the quality of parts should meet the relevant standards, which puts forward high-level requirements for machining quality. Machining quality is mainly composed of two parts: machining accuracy and machining surface quality. Only by strictly controlling the two important links in machining, can the quality of machining be well controlled and the quality of mechanical products reach the use standard.
1. Connotation of machining quality
Machining quality mainly includes two aspects: machining accuracy and machining surface quality, which are affected by the quality of geometry and material respectively.
1.1 quality of geometry in the process of machining, the quality of geometry will affect the accuracy of machining. Geometric quality refers to the geometric error between product surface and interface in the process of machining. It mainly includes two aspects: macro geometry error and micro geometry error. In general, the ratio between wave height and wavelength of macro geometry error is higher than 1000. In general, the ratio of wave height to wavelength is less than 50.
1.2 quality of materials in machining, the quality of materials refers to the changes between the quality of physical properties involved in the surface layer of mechanical products and the matrix, also known as processing modification layer. In the process of machining, the quality of materials will affect the surface quality, which is mainly reflected in the work hardening of the surface layer and the change of the metallographic structure of the surface layer. Among them, the work hardening of surface layer refers to the increase of the hardness of the surface layer metal of mechanical products due to the plastic deformation and sliding between grains during machining. Generally, three aspects need to be considered in the evaluation of machining hardness of mechanical products, namely, surface metal hardness, hardening depth and hardening degree. The change of metallographic structure of surface layer refers to the change of metallographic structure of surface metal of mechanical products due to the action of cutting heat in machining.
2. Influencing factors of machining quality
In the process of machining, machining quality problems mainly include cutting surface roughness and grinding surface roughness. Generally, the factors that affect the quality of machining can be divided into two aspects: geometric factors and physical factors.
2.1 cutting surface roughness in machining, the quality problem of cutting surface roughness mainly includes two aspects: geometric factors and physical factors. Among them, geometric factors include the main deflection angle, sub deflection angle, cutting feed and so on, while physical factors include workpiece material, cutting speed, feed and so on. In machining, ductile materials are used for workpiece processing, the metal plasticity of materials is prone to deformation, and the machined surface will be rough. Therefore, in order to reduce the surface roughness and improve the cutting performance when using medium carbon steel and low carbon steel workpiece materials with good toughness, it is generally necessary to carry out quenching and tempering treatment between finishing.
When machining plastic materials, the cutting speed will have a great impact on the machined surface roughness. When the cutting speed reaches a certain standard, the probability of metal plastic deformation is lower, and the surface roughness is also smaller.
When controlling the cutting parameters, reducing the feed can reduce the surface roughness to a certain extent. However, if the feed rate is too small, the surface roughness will increase; Only by controlling the feed rate reasonably can the surface roughness be reduced.
2.2 grinding surface roughness in the process of machining, the grinding surface is caused by the scoring of abrasive grains on the grinding wheel. In general, if the more sand grains passing through the unit area of the workpiece, the more scratches on the workpiece, and the contour of the scratches on the workpiece affects the surface roughness of grinding. If the contour of the notch on the workpiece is good, the surface roughness of grinding will be lower. In addition, the physical factors that affect the surface roughness of grinding are grinding parameters and so on. In machining, the grinding wheel speed will affect the grinding surface roughness, while the workpiece speed has the opposite effect on the grinding surface roughness. The faster the speed of grinding wheel, the more the number of abrasive particles per unit area of workpiece in unit time, and the smaller the surface roughness. Compared with the speed of grinding wheel, if the speed of workpiece becomes faster, the number of abrasive grains passing through the machined surface of workpiece in unit time will be less, and the surface roughness will be increased. In addition, when the longitudinal feed rate of the grinding wheel is smaller than the width of the grinding wheel, the surface of the workpiece will be cut repeatedly, the roughness of the workpiece will increase, and the surface roughness of the workpiece will decrease.
Post time: May-24-2021
