Built-up edge (BUE) is a common and challenging problem in CNC milling of stainless steel flanges. BUE formation originates from the high temperature and pressure environment of the cutting zone. When the underlying metal of the chip undergoes intense friction and cold welding with the tool rake face, the metal gradually accumulates and hardens, forming a hard lump attached to the tool surface. This phenomenon not only affects machining accuracy, leading to excessive surface roughness, but also accelerates tool wear, shortens tool life, and can even cause cutting vibration, reducing overall machining stability. Therefore, effectively managing the BUE problem is a key aspect of improving the machining quality of CNC milling of stainless steel flanges.
Controlling the cutting speed is one of the core strategies for suppressing BUE. The cutting speed directly affects the temperature distribution in the cutting zone. At medium-speed cutting (usually within a specific range), the temperature conditions are most conducive to the formation and growth of BUE. In this case, the cutting speed can be reduced to a low-speed range or increased to a high-speed range by adjusting the CNC program. At low cutting speeds, the cutting temperature is low, and the plastic deformation of the underlying metal in the chip is weakened, making it difficult to reach the temperature threshold required for cold welding. At high cutting speeds, the cutting temperature rises significantly, the underlying metal in the chip softens, and its shear resistance decreases, making it difficult for built-up edge (BUE) to form. By appropriately selecting the cutting speed, the temperature conditions for BUE formation can be effectively broken, reducing its generation at the source.
Optimizing tool geometry is crucial for controlling BUE. Increasing the tool rake angle reduces friction and cutting forces during the cutting process, lowering the contact pressure between the chip and the tool rake face, thereby weakening the physical basis for BUE formation. Simultaneously, reducing the surface roughness of the tool rake face, through fine grinding or polishing, can reduce the microscopic contact area between the chip and the tool surface, further reducing the coefficient of friction and inhibiting BUE adhesion and growth. Furthermore, using tool materials with higher wear resistance, such as cemented carbide or coated tools, can improve the tool's anti-adhesion ability and extend its service life in a BUE environment.
The selection and application of cutting fluid is an important auxiliary means of managing BUE. High-performance cutting fluids can form a lubricating film between the chip and the tool rake face, effectively reducing the coefficient of friction and minimizing cutting heat. Simultaneously, the cooling effect of the cutting fluid quickly removes heat from the cutting area, preventing localized overheating that could lead to built-up edge formation. In practical applications, extreme pressure cutting oils or emulsions should be selected based on the characteristics of the stainless steel material, ensuring that the cutting fluid is sprayed onto the cutting area with sufficient flow and pressure to fully utilize its lubrication and cooling effects.
Workpiece material pretreatment also has a positive impact on built-up edge control. The high plasticity of stainless steel is a significant contributing factor to built-up edge formation. Heat treatment processes, such as normalizing or tempering, can appropriately increase the hardness of the workpiece material and reduce its plastic deformation capacity, thereby reducing the stagnation and accumulation of the underlying metal in the chips. Furthermore, optimizing the workpiece clamping method to ensure workpiece stability during machining and avoid cutting force fluctuations caused by vibration can also indirectly reduce built-up edge formation.
Optimization of CNC milling processes requires a multi-dimensional, coordinated approach. By rationally planning the toolpath and employing techniques such as layered milling or helical interpolation milling, cutting heat can be dispersed, avoiding localized heat concentration. Simultaneously, optimizing cutting parameter combinations, such as appropriately reducing the feed rate to decrease the cutting thickness, can shorten the chip contact length and weaken the basis for built-up edge growth. Furthermore, introducing online monitoring technology to monitor the temperature and vibration status of the cutting area in real time can provide a basis for dynamic adjustment of process parameters, further improving the stability of the machining process.
Addressing the built-up edge problem in CNC milling of stainless steel flanges requires a multi-pronged approach, including cutting speed control, tool parameter optimization, cutting fluid application, workpiece material pretreatment, and process optimization. Through systematic adjustments and improvements, the formation of built-up edge can be effectively suppressed, improving the quality of the machined surface and tool life, providing a strong guarantee for the high-precision manufacturing of CNC milling of stainless steel flanges.
