Machining surface quality is mainly manifested in the following two aspects: First, there are surface geometry errors such as surface roughness and waviness on the surface of the part; secondly, cold work hardening caused by surface plastic deformation during processing. .
Surface roughness and its influencing factors:
(1) Tool geometry: During the cutting process, the workpiece is plastically deformed by the rounded corner of the tool and the subsequent extrusion and friction, resulting in the theoretical residual area being squeezed and the groove deepened, thus increasing the surface roughness. .
(2) Cutting factors: knife and scale are the main factors affecting roughness.
Changes in physical and mechanical properties of the machined surface and its influencing factors:
1. Cold hardening of the machined surface
(1) Shape factor of the tool: The front angle of the tool, the rounded corners and the amount of wear behind the tool have a great influence on the cold hardened layer. When the rake angle is reduced and the amount of wear at the edge and the back is increased, the depth and hardness of the cold hardened layer are also increased.
(2) Cutting factor: The change of cutting speed and feed rate has a great influence on cold work hardening. When the cutting speed is increased, the contact time between the tool and the workpiece is short, the degree of plastic deformation is small, and the hardened layer and hardness are reduced. The feed rate increases, the degree of plastic deformation increases, and the degree of surface cold hardening increases.
(3) Material to be processed: The hardness of the material to be processed is small, and the more plastic, the more severe the hardening of the material.
2. The action of cutting heat causes the metallographic structure of the machined surface to change, forming a thermal metamorphic layer.
