Surface roughness of CNC machining is one of the important marks to measure the quality of machining surface. It has great influence on wear resistance, corrosion resistance, fatigue strength and fit performance of parts. However, many factors affect the roughness of machined surface. To get good surface roughness, let's understand what these factors are.

Reasons for rough surface of CNC machining:

Residue area: residue area refers to the region left on the machining surface after the primary and secondary cutting edges of the cutting tool.

Two, scalpel: with high-speed steel tool low speed or medium speed cutting plastic metal materials, such as low carbon steel, medium carbon steel, stainless steel, aluminum alloy, often in the processing surface of the knife burr, known as the scalpel. The surface roughness of machined surface will be improved obviously with the appearance of oxidized prickle.

Three, chip accumulation: in the cutting process, when there is chip accumulation, the protruding part can replace the cutting edge into the workpiece, and draw different grooves on the processing surface; When the chips fall off, some of the chips adhere to the machining surface, forming small burrs, resulting in an increase in surface roughness.

Four, vibration: in the cutting process, the machining system produces periodic vibration, stripe or ripple on the machined surface, so that the surface roughness value increases significantly.

The factors affecting surface roughness include residual area, chip, oxide scale, vibration, etc.

First, the tool geometric parameters: the radius of the tool tip arc, the main deflection Angle and the secondary deflection Angle have a great influence on the residual area and vibration. Generally speaking, when the radius of tool tip arc increases, the main and auxiliary declivity angles decrease, the surface roughness value is small. However, if the machine tool stiffness is low, the radius of tool tip arc is too large or the main deflection Angle is too small, the vibration will be generated due to the increase of cutting force, and the surface roughness value will also increase.

Two, cutting tool materials: different cutting tool materials, the size of the radius of the cutting edge arc and keep sharp time is different. HSS tools can grind very sharp edges, but hold time is short, and the surface roughness value is small in low speed cutting. After grinding, the edge arc radius is larger and the surface roughness is smaller at high speed.

Three, cutting amount: the feed has the greatest influence on the residual area. The feed rate decreases and the residual area decreases.

When cutting plastic metals, the surface roughness value is small when the cutting speed is very low or very high. This is because it is not easy to produce chips at low speeds; In high speed cutting, the plastic deformation decreases and the generation of scales can be eliminated. When cutting brittle materials, the effect of cutting speed is very small, because the material deformation is small, so the surface roughness value also decreases.

Four, workpiece material: processing plastic materials, the lower the plasticity of the workpiece material, the higher the hardness, chip accumulation, scale thorn, cold hardness phenomenon less, the smaller the surface roughness value. Therefore, the surface roughness of high carbon steel, medium carbon steel and tempered steel after processing is less than that of low carbon steel. When machining cast iron, the surface roughness of machined cast iron is greater than that of steel under the same machining conditions, because the chip is in the form of chip.