In the processing of patrol automobile instrument parts, surface roughness control is a crucial step in ensuring the functionality and durability of the parts. Surface roughness not only affects the appearance quality of the parts but also directly relates to the accuracy of instrument readings, sealing performance, and long-term stability. Therefore, a comprehensive approach is needed, considering multiple dimensions such as tool selection, cutting parameter optimization, process system stability, workpiece material properties, cutting fluid application, and machining environment control.
Tool geometry parameters have a particularly significant impact on surface roughness. The proper combination of rake angle and clearance angle is key: appropriately increasing the rake angle can improve cutting edge sharpness, reduce cutting forces and plastic deformation, thereby reducing roughness; however, an excessively large rake angle can lead to a decrease in tool strength and cause vibration. The clearance angle reduces friction between the flank face and the machined surface; increasing the clearance angle improves cutting edge sharpness, but an excessively large clearance angle can also weaken tool rigidity and increase the risk of cutting vibration. Therefore, the optimal combination of rake angle and clearance angle needs to be determined experimentally based on material properties and machining requirements. For example, when machining aluminum alloys, a rake angle of 15°-20° and a clearance angle of 8°-12° are suitable.
Optimizing cutting parameters requires a balance between efficiency and quality. Cutting speed, feed rate, and depth of cut are interdependent: low-speed cutting easily generates built-up edge, leading to surface scratches; high-speed cutting, while reducing built-up edge, may cause tool overheating and wear. Insufficient feed rate results in insufficient cutting thickness, with the cutting edge radius compressing the workpiece surface, increasing roughness; excessive feed rate increases the residual area height, also affecting surface quality. In actual machining, the parameter range needs to be determined through trial cuts. For example, during finishing, the cutting speed can be increased to 80-120 m/min, the feed rate controlled at 0.05-0.15 mm/r, and the depth of cut taken at 0.1-0.3 mm, to balance efficiency and surface roughness control.
The stability of the machining system is the cornerstone of surface roughness control. The clearance between the machine tool spindle and the slide plate needs to be adjusted regularly to ensure it is less than 0.04 mm, avoiding vibration caused by excessive clearance. Tool clamping rigidity is equally important. The tool shank should not be too thin, and the tool extension length should be minimized to reduce tool deflection during cutting. For workpiece clamping, slender shaft parts require a center rest or follow rest to prevent bending deformation due to cutting forces, which can lead to surface ripples.
The influence of workpiece material properties on surface roughness cannot be ignored. When machining ductile materials (such as aluminum alloys and low-carbon steel), the compression between the rake face and the workpiece easily forms built-up edge (BUE). The detached BUE leaves hard spots on the workpiece surface, increasing roughness. This can be addressed by optimizing the material's metallographic structure (e.g., tempering low-carbon steel to ferrite plus low-carbon martensite) or adding free-machining elements (such as sulfur and lead) to improve machinability. When machining brittle materials (such as cast iron), it is necessary to reduce the size of graphite particles to avoid pitting from chip fragments on the surface.
The proper application of cutting fluid can significantly improve surface quality. Cutting fluid has cooling, lubricating, and cleaning functions, reducing plastic deformation caused by cutting heat and inhibiting BUE formation. For aluminum alloy machining, extreme pressure emulsions or ionic cutting fluids are recommended, utilizing their excellent penetrability and lubrication to reduce the coefficient of friction. The spray pressure and cleanliness of the cutting fluid must also be controlled to prevent scratches on the workpiece surface caused by impurities.
The stability of the machining environment also affects surface roughness. Temperature fluctuations can cause thermal expansion and contraction of the workpiece, leading to dimensional errors and surface deformation; excessive humidity can easily cause rusting, increasing surface roughness. Therefore, the machining workshop needs to be equipped with a temperature control system and dehumidification equipment to ensure that the ambient temperature is stable at 20-25℃ and the humidity is controlled within the range of 40%-60%. In addition, the cleanliness of the machining area needs to be maintained regularly to prevent dust and chips from adhering to the workpiece surface.
Surface roughness control in patrol automobile instrument parts processing must be integrated throughout the entire process. From the precise selection of cutting tools to the dynamic adjustment of cutting parameters, from the rigidity of the process system to the optimization of workpiece materials, from the scientific application of cutting fluid to the strict control of the machining environment, each link must be quality-centric. Standardized operating procedures should be formed through experimentation and improvement to ultimately achieve efficient control of surface roughness and comprehensive improvement of part performance.
