1, The definition and importance of CNC surface finish
Surface smoothness, also known as surface roughness, is a quantitative indicator of the subtle undulations on the surface of machined parts. It reflects the smoothness of the surface of the part and is an important criterion for evaluating the surface quality of the part. In the CNC machining process, the surface smoothness of the parts not only affects the aesthetics of the parts, but more importantly, it also relates to key performance such as friction performance, wear resistance, corrosion resistance, and fatigue strength of the parts.
CNC machining is known for its high precision and efficiency, capable of manufacturing parts with tolerances as small as 0.025 millimeters. However, as CNC machining belongs to subtractive manufacturing, fine cutting marks may be left on the surface of the finished product during machining, resulting in surface roughness. Therefore, a deep understanding and control of surface smoothness in CNC machining has become an important means to improve product competitiveness.
2, Representation and evaluation of CNC surface finish
There are various ways to represent the surface smoothness of CNC, but the most commonly used is the Ra value (arithmetic mean roughness). The Ra value represents the average deviation of surface micro height, measured in micrometers (μ m). The smaller the Ra value, the smoother the surface and the higher the smoothness.
In practical applications, the evaluation of CNC surface finish usually relies on surface roughness measuring instruments. This instrument measures the height difference between the peaks and valleys of small areas on the surface of the part, calculates the Ra value, and evaluates the surface smoothness of the part.
3, Typical CNC surface finish
The surface smoothness of CNC machining varies depending on factors such as machining methods, workpiece materials, cutting tools, and cutting parameters. Here are some typical CNC surface finish ranges:
CNC turning:
The surface smoothness of general turning is 1.6-0.8 μ m.
When rough cutting, the surface smoothness requirement is 20-10 μ m.
During semi precision and precision machining, the surface finish requirement is 10-0.16 μ m.
The precision grinding diamond turning tool used for high-precision CNC lathes can turn non-ferrous metal workpieces at high speed and precision, with a surface finish of 0.04-0.01 μ m, also known as "mirror turning".
Milling:
The general milling surface finish is 6.3-1.6 μ m.
The rough milling accuracy is 20-5 μ m.
grind:
The general surface finish for grinding is 1.25-0.16 μ m.
The surface finish of precision grinding is 0.16-0.04 μ m.
The surface smoothness of ultra precision grinding is 0.04-0.01 μ m.
The surface smoothness of mirror polishing is less than 0.01 μ m.
Ordinary machine tools and high-speed machines:
The surface finish of a typical CNC machine tool is about 3.2 μ m.
High speed machines can achieve a smoothness of 1.6 μ m.
4, Factors affecting the surface smoothness of CNC
The surface smoothness of CNC is influenced by various factors, including:
Processing methods: Different processing methods (such as turning, milling, grinding, etc.) will produce different surface smoothness.
Workpiece material: The hardness, toughness, and thermal conductivity of the workpiece material can affect the cutting force and cutting temperature during the machining process, thereby affecting the surface finish.
Cutting tools and cutting parameters: The material, shape, cutting edge angle, cutting speed, feed rate, cutting depth, and other cutting parameters of the cutting tool will have a significant impact on the surface smoothness.
Process system: High frequency vibration, tool wear, machine tool accuracy, and other factors in the process system can also affect surface smoothness.
5, Application of CNC surface smoothness
CNC surface finish has a wide range of applications in multiple fields. In the aerospace field, high smoothness surfaces can reduce friction and wear, improve the reliability and durability of parts. In the automotive industry, high surface finish of parts can improve fuel efficiency and vehicle performance. In precision instruments and electronic devices, surfaces with high smoothness can reduce contact resistance, improve conductivity, and enhance heat dissipation.
In addition, the surface smoothness of CNC directly affects the appearance quality and aesthetics of the parts. In the field of consumer goods, such as mobile phones, cameras, and other electronic products, a high surface finish can enhance the product's grade and competitiveness.
