How to avoid built-up edge formation in aluminum CNC turning, which affects machining quality?
Release Time : 2025-12-10
During aluminum CNC turning, the formation of built-up edge (BUE) significantly affects the surface quality, leading to excessive surface roughness, decreased dimensional accuracy, and even abnormal tool wear. Essentially, during aluminum cutting, the intense friction between the chips and the tool rake face causes the underlying material to adhere due to high pressure and temperature, gradually accumulating into a BUE-like structure. This dynamic process of adhesion and detachment continuously scratches the machined surface and alters the actual cutting angle, thus compromising machining stability. Therefore, comprehensive control from multiple dimensions, including cutting parameter optimization, tool selection, cooling and lubrication, process improvement, and equipment maintenance, is necessary to suppress BUE formation.
Selecting the appropriate cutting speed is crucial for suppressing BUE. Aluminum is a ductile material; at excessively low cutting speeds, the contact time between the chips and the tool rake face is prolonged, and frictional heat softens the underlying chip layer, making it more prone to adhesion and BUE formation. Conversely, excessively high cutting speeds cause a rapid increase in cutting temperature, which, while reducing material adhesion, may exacerbate tool thermal wear. Therefore, a suitable cutting speed must be selected based on the aluminum and tool materials. For example, when using carbide tools for 6061 aluminum alloy, controlling the cutting speed within an appropriate range can reduce built-up edge (BUE) formation while ensuring machining efficiency. If using diamond tools, the cutting speed can be appropriately increased to utilize their high thermal conductivity for rapid heat dissipation, further suppressing adhesion.
Optimizing the geometry of aluminum CNC turning tools is crucial for reducing BUE. The rake angle is a major parameter affecting cutting deformation and friction. Increasing the rake angle reduces cutting forces and the contact area between the chip and the rake face, thus reducing the risk of adhesion. However, an excessively large rake angle may lead to insufficient tool strength, so a trade-off must be struck. For example, when turning aluminum, a suitable rake angle is usually chosen to achieve effective cutting while avoiding BUE. Furthermore, the selection of the principal and secondary cutting edge angles must also be considered. A larger principal cutting edge angle reduces the cutting force per unit length of the cutting edge, while a smaller secondary cutting edge angle improves tool wear resistance; the combination of both can reduce the probability of BUE formation.
Improving the cooling and lubrication methods is an effective means of suppressing BUE. While traditional emulsions offer some cooling, their lubrication effect on aluminum is limited, easily leading to chip adhesion. Using extreme pressure cutting oils or micro-volume lubrication (MQL) technology can significantly improve lubrication conditions. Extreme pressure cutting oils form a chemically adsorbed film under high temperature and pressure, reducing direct contact between the tool and chips; MQL technology precisely sprays a micro-mist onto the cutting area, both reducing cutting temperature and forming a lubricating film, effectively suppressing built-up edge (BUE). For example, after adopting MQL technology, one company saw a significant improvement in the surface roughness of machined aluminum, and the BUE problem was essentially eliminated.
Innovative process methods can also reduce the impact of BUE. During climb milling of aluminum CNC turning, the cutting thickness gradually decreases, reducing the contact pressure between the chip and the rake face, thus decreasing the adhesion tendency. Therefore, prioritizing climb milling can suppress BUE. Furthermore, staged cutting processes, by separating roughing and finishing, avoid BUE generated during roughing scratching the machined surface. For example, completing roughing with a larger depth of cut and then finishing with a smaller depth of cut and feed rate can significantly improve surface quality.
Maintaining the condition of equipment is fundamental to ensuring machining stability. Radial runout and axial movement of the machine tool spindle exacerbate cutting vibration, leading to fluctuations in cutting force and promoting built-up edge (BUE) formation. Therefore, it is necessary to regularly inspect and adjust the machine tool's accuracy to ensure smooth spindle operation. Simultaneously, the tool installation accuracy must be strictly controlled to avoid uneven cutting force caused by tool runout. For example, using high-precision tool holders and fixtures can reduce tool vibration and lower the risk of BUE.
Material pretreatment can also indirectly suppress BUE. Oxide layers or impurities on the aluminum surface increase friction and adhesion during cutting. Therefore, the material must be cleaned before machining to remove oil and oxide layers. Furthermore, improving the internal structure of aluminum through heat treatment or cold working can enhance its machinability and reduce BUE formation. For example, solution treatment of certain high-strength aluminum alloys reduces their plasticity, making them more prone to chip formation during cutting and reducing adhesion.