What are the key techniques to improve the surface roughness of precision parts machining?

In precision parts machining, surface roughness has a profound impact on part performance, reliability and service life. In order to enhance the machining surface roughness, can start from the following aspects.

First, the careful selection and maintenance of tools

Tool is a direct effect on the surface of the workpiece tool, its quality and condition of the surface roughness has a huge impact. First of all, to choose high-precision, sharp and wear-resistant tool. For example, in milling processing, the use of coated carbide tools, the coating can reduce the friction coefficient between the tool and the workpiece, reduce chip sticking, so as to obtain a smoother surface. At the same time, the sharpness of the cutting edge of the tool is critical; a dull edge increases the cutting forces, leading to tears and scratches on the machined surface. Therefore, regular sharpening and inspection of the tool is required to ensure that the edge is always in the best condition.

Second, the optimisation of cutting parameters

Cutting parameters include cutting speed, feed and depth of cut. Reasonable selection of these parameters can significantly improve the surface roughness. Cutting speed, for different workpiece materials, there is an optimal cutting speed range. For example, when turning aluminium alloy, an appropriate increase in cutting speed can make the chip formation more continuous and reduce the generation of chip tumour, thus reducing the surface roughness. Feed also needs to be strictly controlled, smaller feed can make the tool on the surface of the workpiece to leave a finer trace, improve surface quality, but too small will affect the processing efficiency. Depth of cut should be reasonably determined according to the size, shape and processing requirements of the workpiece, too large a depth of cut will cause a sharp increase in cutting force, resulting in vibration and surface quality degradation.

Third, the reasonable use of processing technology

Different machining processes have different effects on surface roughness. Take the grinding process as an example, the use of high-precision grinding wheels and reasonable grinding parameters, such as smaller grinding depth and higher wheel speed, can effectively reduce the surface roughness. In addition, the use of advanced machining processes, such as high-speed cutting and micro-lubrication cutting, can also achieve good results. High-speed cutting, the cutting force is reduced, most of the cutting heat is taken away by the chip, which is conducive to improving the surface quality. Micro-lubrication cutting, on the other hand, by applying a small amount of lubricant in the cutting area, to improve the friction state between the tool and the workpiece, reduce cutting heat and tool wear, and then enhance the surface roughness.

Fourth, the guarantee of machine tool accuracy

The precision of the machine tool is to ensure that the processing of the surface quality of the basis. Machine tool spindle rotary accuracy, guideway straightness and flatness of the table will affect the machining surface roughness. Regular precision testing and maintenance of machine tools, timely adjustment and repair of machine tool precision errors. For example, the positioning accuracy of the machine tool is checked by a high-precision laser interferometer, and the motion accuracy of the machine tool is checked by a ballbar to ensure that the machine tool is always in good working condition. At the same time, improving the rigidity of the machine tool and reducing the vibration in the machining process can also effectively improve the surface roughness.

V. Workpiece materials and pretreatment

The quality and performance of the workpiece material has a direct impact on the machining surface roughness. The uniformity of the hardness of the material and the denseness of the internal organisation will affect the cutting process. Therefore, it is necessary to choose workpiece materials with reliable quality and uniform material. Before machining, appropriate pretreatment of the workpiece, such as annealing, normalising and other heat treatment processes, can improve the cutting performance of the material and reduce the surface roughness. For example, spheroidal annealing treatment of high-carbon steel, can make the material hardness reduced and uniform, conducive to cutting and machining, to obtain better surface quality.

Six, the control of the processing environment

The stability of the processing environment should not be ignored. Changes in temperature and humidity will lead to thermal expansion and contraction of the workpiece and machine tool, thus affecting the machining accuracy and surface roughness. Keep the processing workshop temperature and humidity constant, such as temperature control at 20 ℃ ± 2 ℃, humidity control at 40% - 60%, can reduce the error caused by environmental factors. In addition, reducing vibration and dust at the machining site to provide a stable and clean environment for the machining process will help to improve the machined surface roughness of precision parts.